Spectra obtained with the radiative transfer code (model, in red) overlaid to the observations (black) for N₂ H⁺ (1–0) and (3–2) lines. The columns refer to the three models: in the left panels, in the central panels, and in the right ones. The corrective factors f_corr used to modify the whole abundance profile to match the observed fluxes is indicated above the top panel of each column. All models are at t = 10⁶ yr.